Took the ferry out to Alcatraz Island last Saturday (thx, Mija and Henry) to see the old prison and to view the Ai Weiwei installation "@Large". Both the prison and the art were quite powerful. Image above shows "Refraction", a massive sculpture based on the structure of a bird's wing. Feathers are reflective panels used on solar cookers in Tibet. Piece is said "to use the imagery of flight to evoke the tension between freedom and confinement".
Image below shows "Trace", portraits of 175 political prisoners who have been detained because of their beliefs or affiliations. Ai Weiwei calls them "heroes of our time". The portraits are made from Lego bricks. [NOTE: Ai Weiwei also says "we are all potential prisoners"].
And, finally, I offer below a small section of one of the walls in the main cellhouse. Seems like a wonderful desktop image; a high-resolution version can be downloaded here.